Field of the Invention
The present invention relates to an information processing apparatus and a control method therefor.
Description of the Related Art
Information processing apparatuses such as printing apparatuses conventionally have semiconductor integrated circuits, and along with speed-up, density-growth, and digitalization of semiconductor integrated circuits, radiation noise generated due to emission of harmonic energy of a clock signal in the semiconductor integrated circuits to an external of the semiconductor integrated circuit is increasing. Radiation noise interferes with operation of other electronic devices, and hence filters, packages, ferrite beads, or the like are applied to semiconductor integrated circuits, and also, frequency diffusing circuits are used as semiconductor integrated circuits in order to reduce radiation noise generated from semiconductor integrated circuits.
Frequency diffusing circuits add a frequency modulation factor as a several-% tolerance to a specific clock frequency and diffuse harmonic energy, which is generated at the specific clock frequency, in frequency bands outside the range of the frequency modulation factor, thereby reducing radiation noise at the specific clock frequency. For example, when a frequency diffusing circuit adds a frequency modulation factor of 1% to a clock frequency of 100 MHz, harmonic energy generated at 100 MHz is diffused within a range of 99 MHz to 100 MHz to thus reduce radiation noise at 100 MHz.
When a plurality of semiconductor integrated circuits are manufactured, the semiconductor integrated circuits vary in performance, for example, clock frequency. Namely, some of the manufactured plurality of semiconductor integrated circuits operate at high clock frequencies, and others operate at low clock frequencies. Accordingly, there are known semiconductor integrated circuits with an ASV (adaptive supply voltage) function of controlling voltage applied to the semiconductor integrated circuits according to variations in clock frequencies of the semiconductor integrated circuits (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2011-227937).
The semiconductor integrated circuits with the ASV function raise voltage applied to semiconductor integrated circuits with low clock frequencies when they are in use, and on the other hand, lower voltage applied to semiconductor integrated circuits operating at high clock frequencies when they are in use so that operating speeds of the semiconductor integrated circuits can be maintained constant when they are in use. For example, as shown in FIG. 7, a voltage of 1.00 V is applied to a semiconductor integrated circuit with a high clock frequency of 206 MHz, a voltage of 1.06 V is applied to a semiconductor integrated circuit with a moderate clock frequency of 200 MHz, and a voltage of 1.14 V is applied to a semiconductor integrated circuit with a low clock frequency of 192 MHz.
Radiation noise generated from semiconductor integrated circuits increases as voltage values of voltages applied to the semiconductor integrated circuits increase, and decrease as voltage values of voltages applied to the semiconductor integrated circuits decrease. On the other hand, it is known that radiation noise increases as frequency modulation factors added to clock frequencies decrease, and decreases as frequency modulation factors added to clock frequencies increase (see FIG. 8).
However, in semiconductor integrated circuits with the ASV function, frequency modulation factors added to clock frequencies are fixed, and hence the amount of radiation noise generated from the semiconductor intergraded circuits with the ASV function depends on voltages applied to the semiconductor integrated circuits. Therefore, when voltages applied to semiconductor integrated circuits are changed so as to maintain the operating speed of semiconductor integrated circuits constant using the ASV function, a problem arises because the amount of radiation noise from the semiconductor integrated circuits cannot be controlled to be held constant.